Thyroid Agents Flashcards
Describe the mode of action of carbimazole
Inhibit thyroid perioxidase that is responsible for iodinating tyrosyl residues in thyroglobulin to give T3 and T4
Decreased thyroid hormone synthesis
Less sign and symptoms of hyperthyroidism
Why does clinical response for carbimazole take a few weeks?
T4 have a long half life
Takes a while for thyroid stores of hormone to be depleted
How is carbimazole absorbed?
Orally
What is the active form of carbimazole?
Methimazole
How is carbimazole distributed?
Does not bind to plasma protein but is concentrated within the thyroid gland
How is carbimazole metabolized?
Hepatic through CYP and FMO enzymes
How is carbimazole excreted?
Urine (mainly) and feces
What are the adverse drug reactions of carbimazole?
Joint pain
Rashes
Nausea
Jaundice
Agranulocytosis
Hypothyroidism
What is the mode of action of levothyroxine?
Restore body’s T4 to normal levels
How is Levothyroxine absorbed? What special advice should you give patients on levothyroxine?
Orally
Should be taken on an empty stomach to prevent erratic absorption
Avoid medication or food that can affect gastric pH
How is levothyroxine distributed in the body?
High plasma protein binding
How is levothyroxine metabolized? Explain what happens
In the liver and kidneys
Liver: T4 deiodination to T3 occurs through glucuronidation and sulphation
Kidney: Deiodination occurs
How is levothyroxine excreted?
Feces and urine
What are the adverse effects of levothyroxine?
Reduced appetite
Anxiety
Diarrhea
Difficulty sleeping
Hair loss
Heart issues
Seizures
What is the monitoring parameters? How often should it be monitored?
TSH
Monitor 6-8 weeks upon initiation or change in dose
